1. Field of the Invention
The present invention relates to a fuel supply pump and a tappet structure body, and more particularly to a tappet structure body that includes a roller and a tappet body and is disposed so as to be interposed between a plunger and a cam, and to a fuel supply pump disposed with that tappet structure body.
2. Description of the Prior Art
Conventionally, various kinds of pressure-accumulating fuel injection devices that use a pressure accumulator (common rail) to efficiently inject high-pressure fuel in diesel engines and the like have been proposed.
As a fuel supply pump used in such pressure-accumulating fuel injection devices, a fuel supply pump has been employed which includes, for example, a cam integrated with a cam shaft that is rotated by the driving of the engine to be supplied with fuel, a plunger that is raised and lowered by of the rotation of the cam, a tappet structure body that transmits the rotation of the cam as raising force to the plunger, and a spring for applying lowering force to the tappet structure body and the plunger. Further, as the tappet structure body used in such a fuel injection pump, a tappet structure body has been proposed which is configured by a tappet body including a roller housing portion disposed with a sliding surface and by a roller that is held by a pin such that the roller may freely rotate and is housed in the roller housing portion of the tappet body, as shown in JP-A-2001-317430.
However, the tappet structure body disclosed in JP-A-2001-317430 is disposed with a projecting portion in the center portion of the upper surface of the tappet body at the place where it contacts the plunger and has a structure where, when the tappet structure body is raised and lowered, the pressing force loaded from the plunger becomes concentrated in the center portion of the tappet body. For that reason, there have been instances where, at the sliding surface of the roller housing portion of the tappet body, the pressure applied between the housed roller and the sliding surface on which it slides becomes non-uniform and damage occurs at the highest portion of the sliding surface. Consequently, instances have been observed where the durability of the tappet structure body becomes low and where, particularly when used in a fuel supply pump of a pressure-amplifying pressure-accumulating fuel injection device, its lifespan drops.